1. Field of Invention
The present invention relates generally to techniques for treating mitral valve insufficiencies such as mitral valve leakage. More particularly, the present invention relates to systems and methods for treating a leaking mitral valve in a minimally invasive manner.
2. Description of the Related Art
Congestive heart failure (CHF), which is often associated with an enlargement of the heart, is a leading cause of death. As a result, the market for the treatment of CHF is becoming increasingly prevalent. For instance, the treatment of CHF is a leading expenditure of Medicare and Medicaid dollars in the United States of America. Typically, the treatment of CHF enables many who suffer from CHF to enjoy an improved quality of life.
Referring initially to FIG. 1, the anatomy of a heart, specifically the left side of a heart, will be described. The left side of a heart 104 includes a left atrium 108 and a left ventricle 112. An aorta 114 receives blood from left ventricle 112 through an aortic valve 120, which serves to prevent regurgitation of blood back into left ventricle 112. A mitral valve 116 is disposed between left atrium 108 and left ventricle 112, and effectively controls the flow of blood between left atrium 108 and left ventricle 112.
Mitral valve 116, which will be described below in more detail with respect to FIG. 2a, includes an anterior leaflet and a posterior leaflet that are coupled to cordae tendonae 124 which serve as “tension members” that prevent the leaflets of mitral valve 116 from opening indiscriminately. When left ventricle 112 contracts, cordae tendonae 124 allow the anterior leaflet to open upwards until limited in motion by cordae tendonae 124. Normally, the upward limit of opening corresponds to a meeting of the anterior and posterior leaflets and the prevention of backflow. Cordae tendonae 124 arise from a columnae carnae 128 or, more specifically, a musculi papillares of columnae carnae 128.
Left ventricle 112 includes trabeculae 132 which are fibrous cords of connective tissue that are attached to wall 134 of left ventricle 112. Trabeculae 132 are also attached to an interventricular septum 136 which separates left ventricle 112 from a right ventricle (not shown) of heart 104. Trabeculae 132 are generally located in left ventricle 112 below columnae carnae 128.
FIG. 2a is a cut-away top-view representation of mitral valve 116 and aortic valve 120. Aortic valve 120 has a valve wall 204 that is surrounded by a skeleton 208a of fibrous material. Skeleton 208a may generally be considered to be a fibrous structure that effectively forms a ring around aortic valve 120. A fibrous ring 208b, which is substantially the same type of structure as skeleton 208a, extends around mitral valve 116. Mitral valve 116 includes an anterior leaflet 212 and a posterior leaflet 216, as discussed above. Anterior leaflet 212 and posterior leaflet 216 are generally thin, flexible membranes. When mitral valve 116 is closed (as shown in FIG. 2a), anterior leaflet 212 and posterior leaflet 216 are generally aligned and contact one another to create a seal. Alternatively, when mitral valve 116 is opened, blood may flow through an opening created between anterior leaflet 212 and posterior leaflet 216.
Many problems relating to mitral valve 116 may occur and these insufficiencies may cause many types of ailments. Such problems include, but are not limited to, mitral regurgitation. Mitral regurgitation, or leakage, is the backflow of blood from left ventricle 112 into the left atrium 108 due to an imperfect closure of mitral valve 116. That is, leakage often occurs when a gap is created between anterior leaflet 212 and posterior leaflet 216.
In general, a relatively significant gap may exist between anterior leaflet 212 and posterior leaflet 216 (as shown in FIG. 2b) for a variety of different reasons. For example, a gap may exist due to congenital malformations, because of ischemic disease, or because a heart has been damaged by a previous heart attack. A gap may also be created when congestive heart failure, e.g., cardiomyopathy, or some other type of distress causes a heart to be enlarged. When a heart is enlarged, the walls of the heart, e.g., wall 134 of a left ventricle, may stretch or dilate, causing posterior leaflet 216 to stretch. It should be appreciated that anterior leaflet 212 generally does not stretch. As shown in FIG. 2b, a gap 220 between anterior leaflet 212 and stretched posterior leaflet 216′ is created when wall 134′ stretches. Hence, due to the existence of gap 220, mitral valve 116 is unable to close properly, and may begin to leak.
Leakage through mitral valve 116 generally causes a heart to operate less efficiently, as the heart must work harder to maintain a proper amount of blood flow therethrough. Leakage through mitral valve 116, or general mitral insufficiency, is often considered to be a precursor to CHF. There are generally different levels of symptoms associated with heart failure. Such levels are classified by the New York Heart Association (NYHA) functional classification system. The levels range from a Class 1 level which is associated with an asymptomatic patient who has substantially no physical limitations to a Class 4 level which is associated with a patient who is unable to carry out any physical activity without discomfort, and has symptoms of cardiac insufficiency even at rest. In general, correcting for mitral valve leakage may be successful in allowing the NYHA classification grade of a patient to be reduced. For instance, a patient with a Class 4 classification may have his classification reduced to Class 3 and, hence, be relatively comfortable at rest.
Treatments used to correct for mitral valve leakage or, more generally, CHF, are typically highly invasive, open-heart surgical procedures. Ventricular assist devices such as artificial hearts may be implanted in a patient whose own heart is failing. The implantation of a ventricular assist device is often expensive, and a patient with a ventricular assist device must be placed on extended anti-coagulant therapy. As will be appreciated by those skilled in the art, anti-coagulant therapy reduces the risk of blood clots being formed, as for example, within the ventricular assist device. While reducing the risks of blood clots associated with the ventricular assist device is desirable, anti-coagulant therapies may increase the risk of uncontrollable bleeding in a patient, e.g., as a result of a fall, which is not desirable.
Rather than implanting a ventricular assist device, bi-ventricular pacing devices similar to pace makers may be implanted in some cases, e.g., cases in which a heart beats inefficiently in a particular asynchronous manner. While the implantation of a bi-ventricular pacing device may be effective, not all heart patients are suitable for receiving a bi-ventricular pacing device. Further, the implantation of a bi-ventricular pacing device is expensive.
Open-heart surgical procedures which are intended to correct for mitral valve leakage, specifically, involve the implantation of replacement valves. Valves from animals, e.g., pigs, may be used to replace a mitral valve 116 in a human. While the use of a pig valve may relatively successfully replace a mitral valve, such valves generally wear out, thereby requiring additional open surgery at a later date. Mechanical valves, which are less likely to wear out, may also be used to replace a leaking mitral valve. However, when a mechanical valve is implanted, there is an increased risk of thromboembolism, and a patient is generally required to undergo extended anti-coagulant therapies.
A less invasive surgical procedure involves heart bypass surgery associated with a port access procedure. For a port access procedure, the heart may be accessed by cutting a few ribs, as opposed to opening the entire chest of a patient. In other words, a few ribs may be cut in a port access procedure, rather than opening a patient's sternum.
One open-heart surgical procedure that is particularly successful in correcting for mitral valve leakage and, in addition, mitral regurgitation, is an annuloplasty procedure. During an annuloplasty procedure, an annuloplasty ring may be implanted on the mitral valve to cause the size of a stretched mitral valve 116 to be reduced to a relatively not normal size. FIG. 3 is a schematic representation of an annuloplasty ring. An annuloplasty ring 304 is shaped approximately like the contour of a normal mitral valve. That is, annuloplasty ring 304 is shaped substantially like the letter “D.” Typically, annuloplasty ring 304 may be formed from a rod or tube of biocompatible material, e.g., plastic, that has a DACRON mesh covering.
In order for annuloplasty ring 304 to be implanted, a surgeon surgically attaches annuloplasty ring 304 to the mitral valve on the atrial side of the mitral valve. Conventional methods for installing ring 304 require open-heart surgery which involve opening a patient's sternum and placing the patient on a heart bypass machine. As shown in FIG. 4, annuloplasty ring 304 is sewn to a posterior leaflet 318 and an anterior leaflet 320 of a top portion of mitral valve 316. In sewing annuloplasty ring 304 onto mitral valve 316, a surgeon generally alternately acquires a relatively large amount of tissue from mitral tissue, e.g., a one-eighth inch bite of tissue, using a needle and thread, followed by a smaller bite from annuloplasty ring 304. Once a thread has loosely coupled annuloplasty ring 304 to mitral valve tissue, annuloplasty ring 304 is slid onto mitral valve 316 such that tissue that was previously stretched out, e.g., due to an enlarged heart, is effectively pulled in using tension applied by annuloplasty ring 304 and the thread which binds annuloplasty ring 304 to the mitral valve tissue. As a result, a gap, such as gap 220 of FIG. 2b, between anterior leaflet 320 and posterior leaflet 318 may be substantially closed off. After the mitral valve is shaped by ring 304, the anterior and posterior leaflets 320, 318 will reform to create a new contact line and will enable mitral valve 318 to appear and to function as a normal mitral valve.
Once implanted, tissue generally grows over annuloplasty ring 304, and a line of contact between annuloplasty ring 304 and mitral valve 316 will essentially enable mitral valve 316 to appear and function as a normal mitral valve. Although a patient who receives annuloplasty ring 304 may be subjected to anti-coagulant therapies, the therapies are not extensive, as a patient is only subjected to the therapies for a matter of weeks, e.g., until tissue grows over annuloplasty ring 304.
A second surgical procedure which is generally effective in reducing mitral valve leakage involves placing a single edge-to-edge suture in the mitral valve. With reference to FIG. 5a, such a surgical procedure, e.g., an Alfieri stitch procedure or a bow-tie repair procedure, will be described. An edge-to-edge stitch 404 is used to stitch together an area at approximately the center of a gap 408 defined between an anterior leaflet 420 and a posterior leaflet 418 of a mitral valve 416. Once stitch 404 is in place, stitch 404 is pulled in to form a suture which holds anterior leaflet 420 against posterior leaflet 418, as shown. By reducing the size of gap 408, the amount of leakage through mitral valve 416 may be substantially reduced.
Although the placement of edge-to-edge stitch 404 is generally successful in reducing the amount of mitral valve leakage through gap 408, edge-to-edge stitch 404 is conventionally made through open-heart surgery. In addition, the use of edge-to-edge stitch 404 is generally not suitable for a patient with an enlarged, dilated heart, as blood pressure causes the heart to dilate outward, and may put a relatively large amount of stress on edge-to-edge stitch 404. For instance, blood pressure of approximately 120/80 or higher is typically sufficient to cause the heart to dilate outward to the extent that edge-to-edge stitch 404 may become undone, or tear mitral valve tissue.
Another surgical procedure which reduces mitral valve leakage involves placing sutures along a mitral valve annulus around the posterior leaflet. A surgical procedure which places sutures along a mitral valve with be described with respect to FIG. 5b. Sutures 504 are formed along an annulus 540 of a mitral valve 516 around a posterior leaflet 518 of mitral valve 516, and may be formed as a double track, e.g., in two “rows,” from a single strand of suture material. Sutures 504 are tied off at approximately a central point 506 of posterior leaflet 518. Pledgets 546 are often positioned under selected sutures 504, e.g., at central point 506, to prevent sutures 504 from tearing through annulus 540. When sutures 504 are tied off, annulus 540 may effectively be tightened to a desired size such that the size of a gap 508 between posterior leaflet 518 and an anterior leaflet 520 may be reduced.
The placement of sutures 504 along annulus 540, in addition to the tightening of sutures 504, is generally successful in reducing mitral valve leakage. However, the placement of sutures 504 is conventionally accomplished through open-heart surgical procedures. That is, like other conventional procedures, a suture-based annuloplasty procedure is invasive.
While invasive surgical procedures have proven to be effective in the treatment of mitral valve leakage, invasive surgical procedures often have significant drawbacks. Any time a patient undergoes open-heart surgery, there is a risk of infection. Opening the sternum and using a cardiopulmonary bypass machine has also been shown to result in a significant incidence of both short and long term neurological deficits. Further, given the complexity of open-heart surgery, and the significant associated recovery time, people who are not greatly inconvenienced by CHF symptoms, e.g., people at a Class 1 classification, may choose not to have corrective surgery. In addition, people who most need open heart surgery, e.g., people at a Class 4 classification, may either be too frail or too weak to undergo the surgery. Hence, many people who may benefit from a surgically repaired mitral valve may not undergo surgery.
Therefore, what is needed is a minimally invasive treatment for mitral valve leakage. Specifically, what is desired is a method for reducing leakage between an anterior leaflet and a posterior leaflet of a mitral valve that does not require conventional surgical intervention.